Gastroenterology

Gastroenterology

Volume 149, Issue 1, July 2015, Pages 201-210
Gastroenterology

Original Research
Full Report: Basic and Translational—Pancreas
Exclusion of T Cells From Pancreatic Carcinomas in Mice Is Regulated by Ly6Clow F4/80+ Extratumoral Macrophages

https://doi.org/10.1053/j.gastro.2015.04.010Get rights and content

Background & Aims

Immunotherapies that induce T-cell responses have shown efficacy against some solid malignancies in patients and mice, but these have little effect on pancreatic ductal adenocarcinoma (PDAC). We investigated whether the ability of PDAC to evade T-cell responses induced by immunotherapies results from the low level of immunogenicity of tumor cells, the tumor’s immunosuppressive mechanisms, or both.

Methods

KrasG12D/+;Trp53R172H/+;Pdx-1-Cre (KPC) mice, which develop spontaneous PDAC, or their littermates (controls) were given subcutaneous injections of a syngeneic KPC-derived PDAC cell line. Mice were then given gemcitabine and an agonist of CD40 to induce tumor-specific immunity mediated by T cells. Some mice were also given clodronate-encapsulated liposomes to deplete macrophages. Tumor growth was monitored. Tumor and spleen tissues were collected and analyzed by histology, flow cytometry, and immunohistochemistry.

Results

Gemcitabine in combination with a CD40 agonist induced T-cell−dependent regression of subcutaneous PDAC in KPC and control mice. In KPC mice given gemcitabine and a CD40 agonist, CD4+ and CD8+ T cells infiltrated subcutaneous tumors, but only CD4+ T cells infiltrated spontaneous pancreatic tumors (not CD8+ T cells). In mice depleted of Ly6Clow F4/80+ extratumoral macrophages, the combination of gemcitabine and a CD40 agonist stimulated infiltration of spontaneous tumors by CD8+ T cells and induced tumor regression, mediated by CD8+ T cells.

Conclusions

Ly6Clow F4/80+ macrophages that reside outside of the tumor microenvironment regulate infiltration of T cells into PDAC and establish a site of immune privilege. Strategies to reverse the immune privilege of PDAC, which is regulated by extratumoral macrophages, might increase the efficacy of T-cell immunotherapy for patients with PDAC.

Section snippets

Animals

KPC mice have been described previously.12 Trp53LSL-R172H/+, Pdx1-Cre mice are syngeneic healthy littermates generated during routine breeding of KPC mice. All animal protocols were reviewed and approved by the Institute of Animal Care and Use Committee of the University of Pennsylvania.

Cell Lines

Tumor cell lines were developed from tumor tissue obtained from KPC mice as described previously.11

Tumor Studies

Mice were implanted subcutaneously with either a KPC tumor cell line (1 × 106 cells) or a 3 × 3 mm tumor chunk

Combination of Gemcitabine and a CD40 Agonist Produces T-Cell−Dependent Tumor Regressions in a Transplantable Model of Pancreatic Ductal Adenocarcinoma

Strong immunogenic tumor antigens expressed by pancreatic cancer cells arising in KPC mice are currently unknown. Therefore, to induce tumor-specific T-cell immunity, we used a vaccine approach in which gemcitabine chemotherapy is combined with a CD40 agonist.13 To examine this approach, syngeneic littermate Trp53R172H;Pdx-1-Cre mice implanted with pancreatic tumor cell lines derived from immunocompetent KPC mice were treated with gemcitabine and FGK45, an agonist antibody recognizing CD40 (

Discussion

Immune evasion is fundamental to tumor development. Malignant cells can evade immune elimination through a process of immunoediting in which cells adapt to immune pressure by losing their antigenicity and/or by gaining immunosuppressive properties.26 However, increasing evidence supports a role for nonmalignant cells in regulating immune escape in cancer. For example, developing tumors can orchestrate a complex stromal reaction that is immunosuppressive. In PDAC, fibroblasts, TAMs, MDSCs, and

Acknowledgments

The authors are grateful for advice from members of the Beatty and Vonderheide laboratories during preparation of this manuscript. The authors thank Qian-Chun Yu and Hongwei Yu for advice and technical assistance.

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    Conflicts of interest These authors disclose the following: Gregory L. Beatty received research funding from Novartis. Robert H. Vonderheide received research funding from Pfizer and Roche. The remaining authors disclose no conflicts.

    Funding This work was supported by grants from the National Institutes of Health to G.L.B. (NIH K08 CA138907), to R.W. (T32 CA009140), and to R.H.V. (R01 CA169123), from the Damon Runyon Cancer Research Foundation, for which G.L.B. is Nadia's Gift Foundation Innovator of the Damon Runyon-Rachleff Innovation Award (DRR-15-12), a Molecular Biology and Molecular Pathology and Imaging Cores of the Penn Center for the Molecular Studies in Digestive and Liver Diseases grant (P30 DK050306) from the Pancreatic Cancer Action Network and American Association of Cancer Research (R.H.V.), and by the Abramson Family Cancer Research Institute (R.H.V.).

    Author names in bold designate shared co-first authorship.

    Authors share co-second authorship.

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